1. Field
This application relates to internal combustion engines, specifically to variable displacement engines.
2. Prior Art
An internal combustion heat engine is needed to convert chemical energy to mechanical power. These type of engines are very popular due to a number of factors such as ease of refueling, quick refuel times and typical range of hundreds of miles. Engines are designed for a vehicle based mainly on vehicle weight, the larger the vehicle, the larger the engine required. Typically, an internal combustion engine is designed with a fixed displacement. Unfortunately, the larger the displacement, the more work is required to push against the atmosphere. Since full power capacity is not required at all times, it would be desirable to have an engine with a variable displacement. An engine with variable displacement could reduce its displacement to conserve energy when traveling at low speeds, or downhill, or coasting to a stop. An engine with variable displacement could also increase its displacement when needed, such as when moving uphill, accelerating, traveling at high speed, or carrying a heavy load.
Prior art uses a variety of techniques to vary displacement: axial engines, z cranks, active cylinder management, cam on crankshaft, rocker rod, and many others. One technique is active cylinder management, that controls displacement by turning off and on fuel supply to cylinders, for example in U.S. Pat. No. 4,494,503 (1985) to Danno. Active cylinder management while somewhat practical, suffers from a small savings of approximately 15%, because all cylinders still must work against the atmosphere. Another technique achieves variable displacement by varying the stroke of a piston. A prior art example of stroke adjustment varies the angle of a rotating plate on the crankshaft connected to axially mounted cylinders, U.S. Pat. No. 5,113,809 (1992) to Ellenburg. The angled plate design has too many drawbacks to be useful, being very difficult to adjust displacement under power, bulky design, and excessive vibration. Another technique achieves variable displacement by varying the stroke of the piston in U.S. Pat. No. 6,938,589 (2005) to Park, by adjusting an angled crankshaft, or the Z type crankshaft. The angled crankshaft technique would be prone to balance problems resulting in undesired vibrations and cylinders with different simultaneous stroke lengths, resulting in decreased energy savings. The Z type crankshaft in U.S. Pat. No. 6,938,589 would have to be much longer than a conventional crankshaft, and would result in a very large and massive engine. Another problem in U.S. Pat. No. 6,938,589 would be lack of controlling displacement under power, as the design does not explain how large forces from engine torque would be overcome during adjustment, namely between the piston and sliding crankshaft. U.S. Pat. No. 6,938,589 also does not explain how the engine will maintain balance or compression ratio adjustments while adjusting the displacement. Another example of prior art, in U.S. Pat. No. 5,406,911 (1995) to Hefly, controls displacement and independently controlling compression ratio by rotating a cam on the crankshaft and adjusting piston arm length by rotating the piston. While U.S. Pat. No. 5,406,911 is the most sound of all prior art examples, there are three major flaws in the design. The first flaw is the adjustment of displacement using a rotating cam on crankshaft will result in a timing error with respect to crankshaft, valves, and ignition timing. Another flaw is the adjustment requires the use of a servo motor mounted on the crankshaft where electric power and electronic signals would be difficult to route to while the crankshaft rotates. Another flaw that could perhaps be fixed easily is the piston arm adjustment uses a gear meshing with an elongated piston. The increased piston cylinder will increase the engine size modestly, however the biggest flaw in this design is the friction between the gear and cylinder would quickly wear the gear and piston, resulting in decreased engine and piston arm control life. A technique that can finely adjust the piston stroke of the engine would be highly desirable, as it would allow greater savings in energy than other designs. A design that has the most control over piston stroke length would be the most desirable of these type of variable displacement engines. A design with the most compact, and least amount of vibrations is also desirable. A design that can adjust all cylinders to the same stroke length would be desirable. A design that uses positively engaged mechanical means to adjust the stroke length is preferred over designs that use hydraulics, pneumatics and friction, that are prone to shortened life due to increased wear of parts.